At the beginning of the Second World War the Royal Navy had no major bases in Northern Ireland and the three Irish bases, at Cork, Berehaven and Lough Swilly, had been handed over to the Irish government in 1938. There was a small base on the Bann at Coleraine at which a motor launch flotilla had its headquarters. Although the Admiralty had instituted a convoy system for merchant ships before war broke out, it was expected that convoys coming to Britain from Canada, the United States and elsewhere would pass Ireland through the south-western approaches, enter St George’s Channel via the Celtic Sea and then sail into the Bristol Channel for Avonmouth or the Irish Sea for Liverpool or Glasgow. No necessity was seen for locating significant naval forces in Northern Ireland.

That changed with the fall of France in June 1940. German U-boats no longer had to sail from their bases on the German coast through the North Sea and around the north of Scotland to reach their patrol areas in the Atlantic. They could now use the great naval bases on the Atlantic coast of France, Brest, St Nazaire, la Pallice and Lorient, thereby increasing their time in the Atlantic and making the sea area off south-west Ireland a death trap for merchant ships.

The Admiralty immediately ordered convoys to be re-routed through the north-western approaches which would take them around the north coast and through the North Channel to the Irish Sea. But the problem of escorting those convoys to ensure their ‘safe and timely arrival’ remained almost as great. There was an acute shortage of escort ships and those ships that were available were short-range vessels. It became imperative to establish an escort base as far west in the United Kingdom as possible. There was one obvious location: Londonderry, where the Port and Harbour Commissioners had recently made the navigable channel of the River Foyle and Lough Foyle deeper.

Londonderry had already been identified as a location for a refuelling station and destroyer repair base. It was also suitable for use by escort ships and plans were made for expansion of the dock facilities in the city and downriver at Lisahally to accommodate such ships. But there was one major problem: where was the border between the UK and Ireland? On land there was no question but a problem arose because Lough Foyle lies between Counties Londonderry and Donegal and, except for a short stretch, so also does the River Foyle.

Although the question might have been even more complicated by the belief that the Anglo-Irish Treaty had given jurisdiction over the waters around Ireland to the new government in Dublin, this was not considered a major factor since the same Treaty had given the Royal Navy the responsibility of protecting those waters. But if the border between the UK and Ireland ran through Lough Foyle then the UK government might face serious objections from the Irish government about the intention to establish a major naval base on the Foyle. While the Irish authorities could not prevent Royal Navy vessels sailing into the Foyle there was potential for considerable embarrassment. The UK had gone to war in the wake of a small country, Poland, being attacked by its much larger neighbour, Germany; and Britain using its naval strength to overcome Irish objections might be portrayed in a similar light, especially in the United States where many Irish-Americans maintained a strong anti-British attitude.

On 31 August 1940, Sir John Maffey, the UK representative to the Irish government, wrote to the Dominions Office in London that ‘use by Admiralty of Lough Foyle should from now on be constant but for the present on limited scale so that user may be established quietly if possible. My inclination is to make no communication on the subject to the Eire Government, to wait on events and to let them know when and if use on large scale is intended. So far as naval use is concerned we appear to have [a] good case.’ So it seemed that the intention was to make increased use of the Foyle unless the Irish Government made strong objections.

In September 1940 Maffey approached the Irish External Affairs Secretary, Joseph Walshe, to inform him ‘of the intended increase of light naval craft’ in Lough Foyle and that flying boats would use Lough Foyle ‘from time to time’. By then the motor launch flotilla from Coleraine had been moved to the city and some larger vessels had already come to Londonderry. He asked that the ‘Eire Government … take a sympathetic view when our aircraft failed to hold off completely from the Donegal shore’ because of wind conditions. Maffey informed London that Walshe had made notes of both matters ‘but made no comment and I left without further discussion’. He believed that this was a satisfactory ‘first round’ and suggested that a flying boat ‘puts in at Lough Foyle at an early date if convenient’.

Arrangements were made for a flying boat to land on Lough Foyle ‘remaining there for about 30 minutes’. The captain of the aircraft was instructed that if ‘approached by officials of Eire Government he is to reply that he had been forced to land owing to engine trouble and would take off again as soon as the fault had been rectified’. The excuse proved unnecessary.

The Royal Navy increased its use of Lough Foyle in the early months of 1941. At the same time, Maffey reported to London that he had been ‘summoned to an interview’ with the Taoiseach, Eamon de Valera, at noon on 20 January 1941 about the establishment of an air corridor over Donegal, in the area of Ballyshannon, that would allow Allied aircraft to use Lough Erne in County Fermanagh as a base from which to patrol the Atlantic sea lanes and provide protection for convoys. This became known as the ‘Donegal Corridor’. During the same meeting de Valera agreed to the use of the flying-boat base at Foynes, close to the modern Shannon airport, ‘for civil aviation purposes by oversea flying boats flying to Lisbon, West Africa and America.’ It was Maffey’s opinion that these concessions furnished proof of an Irish desire ‘to help in directions which do not involve obvious dangers here of German reprisals’.

The Royal Navy remained concerned that there might be a challenge to its use of the Foyle on the grounds that ships navigating the river to Lisahally and Londonderry might be infringing Irish neutrality. If the border followed the median line of Lough Foyle then the channel might be in Irish waters as it ‘lies near to the Eire shore’. In mid-November 1941, the Naval Officer-in-Charge (NOIC), Londonderry, Captain Philip Ruck-Keene, reported to the Admiralty the results of a consultation with the solicitors to the Honourable The Irish Society. He commented that ‘These papers may be of interest should a controversy arise with the Eire authorities, not that any such is anticipated.’

What had Ruck-Keene discovered? The Irish Society solicitors had informed him that the border between Counties Londonderry and Donegal, and therefore between the United Kingdom and Éire did not follow the median line of Lough Foyle. Instead, that border followed the north side of Lough Foyle ‘from Culmore Fort down to Greencastle’. To support this argument the Irish Society had examined the history of County Londonderry which was ‘constituted out of the lands etc granted to the Hon. The Irish Society on behalf of the City of London in 1613 (confirmed in 1662) and among these lands was the bed and soil of the whole of Lough Foyle and of the river up to the utmost flow of the tide at Lifford’. It followed that, since ‘the whole of Lough Foyle’ was included in County Londonderry, the Londonderry/Donegal border could not be the ‘ad medium filum line’ in the lough.

It was pointed out that the Northern Ireland Courts had exercised jurisdiction over all of Lough Foyle in an undefended action, although there was a possible objection: the difficulty of tracing ‘Acts of recognition supporting the inclusion of the Lough in Co. Londonderry during the three centuries since the grant of the Charter’. This had never been a problem while Ireland was a single entity and nor would it have been a problem had de Valera’s government joined in the war on the Allied side. But the prevailing circumstances had the potential to create embarrassment for Britain.

However, there had been an act of parliament in 1838 which did recognise Lough Foyle as part of County Londonderry. This was ‘An Act for draining and embanking certain Lands in Lough Swilly and Lough Foyle in the Counties of Donegal and Londonderry’, dated 27 July 1838. The opening paragraph of the Act had noted that ‘the Lakes or Loughs called respectively Lough Swilly and Lough Foyle, situate respectively in the Counties of Donegal and Londonderry’ had mud banks or ‘slobs’ which were covered by tidal waters and, therefore, unable to be cultivated and of little value. Under the Act certain persons, referred to as Undertakers, were authorised, at their own expense, to embank, drain and cultivate these slobs. The effect of this act was to recognise that the land between low and high tide on the north side of Lough Foyle was also part of County Londonderry although there are no ‘slobs’ on this side of the lough.

The Irish Society also quoted the Charter of King Charles II in 1662 which defined fishing rights in the ‘whole water, bay, river, stream, or rivulet, of Loughfoile within the limits aforesaid … from the high sea unto the town of Liffer, and to the utmost flux and reflux of the river of Loughfoile aforesaid, and in, through, and within the whole course of the water within the limits aforesaid, being in the county of the city of Derry, otherwise Londonderry, and in the counties of Coleraine, Tirone, and Donegall, otherwise Londonderry aforesaid, or in any or some of them, within the said province of Ulster’. (Until the Plantation there had been no county called Londonderry; this was created by adding pieces of Donegal, Tyrone and Antrim to the former Coleraine County.)

With the information provided by the Irish Society the Royal Navy felt confident that it had not infringed any international frontier by establishing its base on the Foyle. Since the Irish Government never challenged the use of that base by the Allied navies it seems that they, too, accepted that there was no legal argument. When the war ended the Royal Navy continued to maintain a base on the Foyle and did so until 1970 when it was finally closed as a result of changes in defence policy.

More recently the British and Irish governments have created the Loughs Agency, a body that promotes the development of the waters of Lough Foyle and Carlingford Lough for commercial and recreational purposes. The agency also has responsibilities for the management of the inland fisheries of both areas. That such a body exists suggests that neither government is likely ever to dispute the ownership of the waters of either lough as seemed possible during the early days of the Second World War.